Re: Rename max_parallel_degree? - Mailing list pgsql-hackers

From David G. Johnston
Subject Re: Rename max_parallel_degree?
Date
Msg-id CAKFQuwaOBi6RYV-sOsn2kz_yswtee=23v9rzHmT-Q0MShYTikA@mail.gmail.com
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In response to Re: Rename max_parallel_degree?  (Robert Haas <robertmhaas@gmail.com>)
List pgsql-hackers
On Tue, May 31, 2016 at 3:35 PM, Robert Haas <robertmhaas@gmail.com> wrote:
On Tue, May 31, 2016 at 3:19 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> I wrote:
>> At the risk of opening another can of worms, what about renaming
>> max_worker_processes as well?  It would be a good thing if that
>> had "cluster" in it somewhere, or something that indicates it's a
>> system-wide value not a per-session value.  "max_workers_per_cluster"
>> would answer, though I'm not in love with it particularly.
>
> Actually, after a bit more thought, maybe "max_background_workers" would
> be a good name?  That matches its existing documentation more closely:
>
>          Sets the maximum number of background processes that the system
>          can support.  This parameter can only be set at server start.  The
>          default is 8.
>
> However, that would still leave us with max_background_workers as the
> cluster-wide limit and max_parallel_workers as the per-query-node limit.
> That naming isn't doing all that much to clarify the distinction.

It sure isn't.  Also, I think that we might actually want to add an
additional GUC to prevent the parallel query system from consuming the
entire pool of processes established by max_worker_processes. 

​My mind started going here too...though the question is whether you need a reserved pool or whether we apply some algorithm if (max_parallel + max_other > max_cluster).  That algorithm could be configurable (i.e., target ratio  20:10 where 20+10 == max_cluster).

David J.

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